DESCRIPTION(adapted from applicant's abstract): Studies in this application propose to investigate this apparent synergistic relationship between HSPG and LRP or megalin, that is necessary for lipoprotein/lipase clearance by cells. Using quantitative biochemical procedures we will determine if ligands are 1) transferred to the endocytic receptors for internalization following their initial binding to HSPG, or 2) if the HSPG and endocytic receptors are cointernalized with bound ligand. These studies will aid in determining if LRP and megalin can regulate ligand sequestration or lipolytic enzyme activities by controlling the amount of HSPG that is present on the cell surface through endocytosis. We also plan to identify the proteoglycan-like molecule that coprecipitates with megalin and LRP, and determine if disrupting its interactions with LRP and megalin prevents the uptake of lipoproteins by cells. As a second goal, studies are proposed to quantitatively evaluate the changes in LRP and megalin expression during adipocyte differentiation, and assess the functional role of these receptors in intracellular lipid accumulation. Supporting data have found that expression of LRP and megalin in differentiating adipocytes is responsive to glucocorticoid- and cAMP-dependent signaling pathways. Based on this observation the applicant plans to identify and characterize the cis- and trans-activating elements in the promoters of LRP and megalin that are responsible for regulating their expression levels during adipocyte development. Together, these studies will help 1) better define the functional roles of LRP and megalin in lipoprotein clearance, 2) begin to understand the molecular basis of their tissue-specific expression, and 3) advance our knowledge of cardiovascular health and disease such as atherosclerosis and obesity.